The structural and functional organization of the vertebrate retina will be investigated by a combination of intracellular electrophysiological recording, intracellular dye injection and analysis of serial thin sections. The intensive application of these methods in the same retina is expected to reveal specific details of the neuronal circuitry in the inner plexiform layer underlying the receptive field characteristics of retinal ganglion cells. New information about the functional stratification and neuronal circuitry of the inner plexiform layer of the mudpuppy retina will be described, in the extenion of previous work. Previously unknown information will be discovered about the physiology and ultrastructure of neurons in the uniquely regular mosaic inner plexiform layer of the cichlid fish.